Years ago, at a party while I was at university, the conversation turned (as
it sometimes does after a lot of alcohol has been consumed) to lateral
thinking puzzles, mostly involving people dying is ways that make murder
look like suicide - or indeed suicide look like murder, and involving people
of restricted stature, failed tape recordings, piles of sawdust or puddles
of water.

One person said "More people die on their birthday than any other day. Why
is this?" This was presented as if it were a fact. We had no way of knowing
whether it was indeed the case - it was long before Wkipedia and articles
such as https://en.wikipedia.org/wiki/Birthday_effect which describe the
effect and give various medical reasons.

We tried all the obvious things like "does this include babies that are born
dead or who die within a few hours" and "does it include alcohol-related
accidents when people do stupid things at their birthday party". No, we were
told. We were over-thinking the problem and over-complicating it. The reason
was blindingly obvious. The question became really quite smug (to the point
that I could see some of my mates were itching to punch his lights out!) and
said that the teacher had asked the question when he was a lad at school;
although he'd never been asked it before or even thought about it, he got
the answer immediately. He was amazed than none of us could work it out. "Is
this true in all cultures?" "Is it true even if you don't know the date and
therefore whether today is your birthday?" He just smiled smugly and
repeated that we were thinking far too deeply and analytically about it.

Sadly we never did find out the answer: it was left as "I'll let you think
about it. Come and tell me when you eventually work out the answer" and I
never saw him again.

Can anyone think of a logical reason, which doesn't involve alcohol-related
accidents, people who are terminally ill holding out until their next
birthday, depression/suicide "I'm a year older than I was" etc? Something
which is "blindingly obvious" even to a ten-year-old at school?